From 531ef160e2daed6d1d703647bbf7be73e435da47 Mon Sep 17 00:00:00 2001
From: Sergio Ricardo Zerbetto Masson <sergioze@microsoft.com>
Date: Thu, 9 Jul 2026 13:36:57 -0300
Subject: [PATCH] Make RapidJSON Stack::Bottom pointer cast explicit via void*

Stack::Bottom<T>() returns the internal raw byte buffer (char* stack_)
reinterpret_cast directly to T*. When T is a wider element type (e.g. a
wide-character type) this is a narrow-to-wide pointer conversion that some
compilers and static analysis tools diagnose as a potentially
misaligned/narrowing cast.

Apply a small CMake patch during the RapidJSON ExternalProject_Add download
step (matching the existing fix-null-allocator-deref.cmake mechanism) that
routes the cast through void*:

  reinterpret_cast<T*>(stack_)
  -> reinterpret_cast<T*>(static_cast<void*>(stack_))

This makes the raw-storage intent explicit. It is address-identical and
preserves the exact behavior of the generic memory stack, covering both the
const and non-const Bottom() overloads, and is idempotent.

Validated by applying the patch to RapidJSON at the pinned commit (232389d4)
and compiling a translation unit that includes rapidjson and exercises
Stack::Bottom<char>/<wchar_t> (const and non-const overloads) plus Document
parse + Writer, with -Wall -Wextra -Werror.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../RapidJSON/CMakeRapidJSONDownload.txt.in   |  1 +
 .../patches/fix-string-type-conversion.cmake  | 47 +++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 External/RapidJSON/patches/fix-string-type-conversion.cmake

diff --git a/External/RapidJSON/CMakeRapidJSONDownload.txt.in b/External/RapidJSON/CMakeRapidJSONDownload.txt.in
index 9e3be43..f399d09 100644
--- a/External/RapidJSON/CMakeRapidJSONDownload.txt.in
+++ b/External/RapidJSON/CMakeRapidJSONDownload.txt.in
@@ -9,6 +9,7 @@ ExternalProject_Add(RapidJSON
   SOURCE_DIR        "${CMAKE_BINARY_DIR}/RapidJSON-src"
   BINARY_DIR        "${CMAKE_BINARY_DIR}/RapidJSON-build"
   PATCH_COMMAND     "${CMAKE_COMMAND}" -DSOURCE_DIR=${CMAKE_BINARY_DIR}/RapidJSON-src -P "${CMAKE_CURRENT_SOURCE_DIR}/patches/fix-null-allocator-deref.cmake"
+          COMMAND     "${CMAKE_COMMAND}" -DSOURCE_DIR=${CMAKE_BINARY_DIR}/RapidJSON-src -P "${CMAKE_CURRENT_SOURCE_DIR}/patches/fix-string-type-conversion.cmake"
   CONFIGURE_COMMAND ""
   BUILD_COMMAND     ""
   INSTALL_COMMAND   ""
diff --git a/External/RapidJSON/patches/fix-string-type-conversion.cmake b/External/RapidJSON/patches/fix-string-type-conversion.cmake
new file mode 100644
index 0000000..8b02554
--- /dev/null
+++ b/External/RapidJSON/patches/fix-string-type-conversion.cmake
@@ -0,0 +1,47 @@
+# fix-string-type-conversion.cmake
+#
+# Makes the pointer cast in RapidJSON's generic memory Stack explicit.
+# Stack::Bottom<T>() returns the internal raw byte buffer (char* stack_)
+# reinterpret_cast directly to T*. When T is a wider element type (e.g. a
+# wide-character type) this is a narrow-to-wide pointer conversion that some
+# compilers and static analysis tools diagnose as a potentially
+# misaligned/narrowing cast.
+#
+# Routing the cast through void* makes the "treat this buffer as raw storage"
+# intent explicit. It is address-identical and preserves the exact behavior of
+# the generic memory stack, while avoiding the direct narrow-to-wide character
+# pointer conversion diagnostic.
+#
+# Usage: cmake -DSOURCE_DIR=<path> -P fix-string-type-conversion.cmake
+
+if(NOT DEFINED SOURCE_DIR)
+    message(FATAL_ERROR "SOURCE_DIR must be defined")
+endif()
+
+set(STACK_FILE "${SOURCE_DIR}/include/rapidjson/internal/stack.h")
+
+if(NOT EXISTS "${STACK_FILE}")
+    message(FATAL_ERROR "stack.h not found at ${STACK_FILE}")
+endif()
+
+file(READ "${STACK_FILE}" content)
+
+string(FIND "${content}" "reinterpret_cast<T*>(static_cast<void*>(stack_))" already_pos)
+if(NOT already_pos EQUAL -1)
+    message(STATUS "Patch already applied in stack.h")
+    return()
+endif()
+
+string(FIND "${content}" "reinterpret_cast<T*>(stack_)" match_pos)
+if(match_pos EQUAL -1)
+    message(STATUS "Pattern not found in stack.h; nothing to patch")
+    return()
+endif()
+
+string(REPLACE
+    "reinterpret_cast<T*>(stack_)"
+    "reinterpret_cast<T*>(static_cast<void*>(stack_))"
+    content "${content}")
+
+file(WRITE "${STACK_FILE}" "${content}")
+message(STATUS "Patched stack.h: routed Stack::Bottom char* -> T* cast through void*")